1) Let's analyze the following equations.
a)
So we can tell that there are infinitely many values for x that times 0 yields 0.
b)
There is one solution.
c), d) Note that whenever there is the same value for the x-term we can tell that this is going to yield 0x and therefore there will be infinitely many solutions. That is the case, in a, c, d
All of them are going to end up with 0x=0,